The present invention relates generally to the art of electric motors and other electromechanical machines. More particularly, the invention relates to an improved winding arrangement for the stator of an electromechanical machine.
Electric motors and other electromechanical machines are generally constructed having a cylindrical stator core. The inner circumference of the stator core defines a plurality of radial slots in which electrical windings are maintained. As is well known, current flow through the windings produces a rotating magnetic field which the rotor of the machine will tend to follow.
The stator windings of an AC induction motor are typically arranged into a plurality of coil groups, with each coil group providing a single pole of a single phase. Each side of an individual coil typically shares a particular winding slot with one side of another coil in a different coil group. Thus, a common three-phase, two-pole induction motor will have a total of six coil groups. Typically, each of the coil groups in such a motor will be configured having eight coils, yielding a total of forty-eight coils. These forty-eight coils have a total of ninety-six coil sides, located in forty-eight winding slots.
The art has developed several winding patterns in which the coil groups can be arranged. For example, one arrangement that has seen widespread use in industry is the “lap winding.” In this arrangement, one side of a coil will be in the “bottom” of a particular winding slot, while the other side of the same coil will be positioned in the “top” of another slot several slot positions away. Moreover, the respective sides of every coil will be separated by the same number of slot positions. Thus, the individual coils overlap each other around the inner circumference of the stator core.
Another common winding arrangement is referred to as a “concentric winding.” In this type of arrangement, coils within a group are organized concentrically, such that sides of each coil will be separated by a different number of slot positions.
“Lap windings” and “concentric windings” each offer certain advantages not offered by the other. For example, lap windings typically exhibit outstanding operational characteristics. The lap winding process, however, has been extremely difficult to automate. Concentric windings, on the other hand, are amenable to automation. Thus, concentric windings are often preferred when motor cost is a significant factor.
While cost considerations tend to make the use of concentric windings desirable, it has not been possible to provide concentric windings in all motor sizes. For example, it has been found necessary to manually wind motors of 200 HP or larger with a lap winding pattern. This is due to the nature of a concentric winding pattern, in which the motor's lead wires must be attached to only one side of the stator core. With the large lead wires required at higher power levels, a standard frame size, such as a NEMA 440 frame, simply does not provide sufficient clearance to route the lead wires to the frame's conduit box opening. A lap winding pattern permits smaller lead wires to be connected at each end of the stator core, which are more easily routed to the conduit box opening in the frame.